Delete unused methods of the VideoProcessing class. And fix a typo.

Rename EnableDenosing --> EnableDenoising.
Delete VideoProcessing FrameStats methods.
Delete VideoProcessingImpl::BrightnessDetection and related files.
Delete VideoProcessingImpl::Deflickering and related files.
Delete VideoProcessing::Brighten.

BUG=

Review URL: https://codereview.webrtc.org/1901393003

Cr-Commit-Position: refs/heads/master@{#12521}
diff --git a/webrtc/modules/video_processing/frame_preprocessor.cc b/webrtc/modules/video_processing/frame_preprocessor.cc
index 406119e..7393af8 100644
--- a/webrtc/modules/video_processing/frame_preprocessor.cc
+++ b/webrtc/modules/video_processing/frame_preprocessor.cc
@@ -22,7 +22,7 @@
   spatial_resampler_ = new VPMSimpleSpatialResampler();
   ca_ = new VPMContentAnalysis(true);
   vd_ = new VPMVideoDecimator();
-  EnableDenosing(false);
+  EnableDenoising(false);
   denoised_frame_toggle_ = 0;
 }
 
@@ -87,7 +87,7 @@
   return spatial_resampler_->TargetHeight();
 }
 
-void VPMFramePreprocessor::EnableDenosing(bool enable) {
+void VPMFramePreprocessor::EnableDenoising(bool enable) {
   if (enable) {
     denoiser_.reset(new VideoDenoiser(true));
   } else {